1. Field of the Invention
The present invention generally relates to light source driving devices, and particularly to a light source driving device with a full-bridge circuit.
2. Description of Related Art
Liquid Crystal Display (LCD) panels generally use discharge lamps, especially Cold Cathode Fluorescent Lamps (CCFLs) as light sources of the backlight systems thereof. Typically, the CCFL is driven by an inverter that supplies AC signals. For larger LCD panels, long-type CCFLs are employed to achieve a desired brightness. In practical applications, the long-type CCFL should be driven by two high-voltage driving means to achieve even brightness.
FIG. 7a is a plane view of a currently existing electronic device 6, and FIG. 7b is a F-direction side view of FIG. 7a. The electronic device 6 comprises a LCD panel 610 and a two high-voltage discharge lamp driving devices. The two high-voltage discharge lamp driving devices are provided for driving a plurality of discharge lamps 64 disposed in the LCD panel 610 in parallel (as shown in FIG. 7b), which comprises a first control circuit board 61, a second control circuit board 61′, a set of signal lines 612. The first control circuit board 61 is configured with a plurality of connectors 622, a first balancing circuit 62, and a first control circuit 63. The first balancing circuit 62 comprises a plurality of inductance element 621 respectively connected to one end of each of the discharge lamps 64. The second control circuit board 61′ is configured with a plurality of connectors 622′, a second balancing circuit 62′, and a second control circuit 63′. The second balancing circuit 62′ comprises a plurality of inductance elements 621′ respectively connected to another end of each of the discharge lamps 64.
The first control circuit 63 is disposed on the first control circuit board 61, and is used for converting a received electrical signal to a first electrical signal that can drive the discharge lamps 64. The first balancing circuit 62 is also disposed on the first control circuit board 61, and is connected to the first control circuit 63 for balancing currents flowing through the discharge lamps 64. The first control circuit board 61 is connected to the discharge lamps 64 by way of the connectors 622. The second control circuit 63′ is disposed on the second control circuit board 61′, and is used for converting a received electrical signal to a second electrical signal that can drive the discharge lamps 64.
The second balancing circuit 62′ is also disposed on the second control circuit board 61′, and is connected to the second control circuit 63′ for balancing currents flowing through the discharge lamps 64. The second control circuit board 61′ is connected to the discharge lamps 64 by way of the connectors 622′. The first control circuit board 61 is connected to the second control circuit board 61′ by way of the signal lines 612, and transmits a synchronization signal for the first control circuit 63 of the first control circuit board 61 to the second control circuit 63′ of the second control circuit board 61′.
The two high-voltage discharge lamp driving devices convert the received signal (about 24V) to an AC signal that can drive the discharge lamps, which is defined as a low voltage driving means.
Another currently existing two high-voltage discharge lamp driving devices not only comprise the elements of the electronic device 6 of FIG. 7a, but comprise a first power factor correction circuit (Power Factor Correction, PFC) and a second PFC circuit. Each of the PFC circuits directly receives a local AC signal, such as 220V in Mainland China, and 110V in North America, and converts the AC signal to a DC signal of about 400V by use of the PFC circuits, and transmits the DC signal to an inverter circuit to light the discharge lamps. In contrast to the low voltage driving means, the driving means is defined as a high voltage driving means. The high voltage driving means has high efficiency due to omitting the circuit for converting a 400V signal to a 24V signal.
With said two driving means, the discharge lamp driving devices drive the discharge lamps 64, both by using the high voltage signals generated by the first control circuit 63 of the first control circuit board 61 and the second control circuit 63′ of the second control circuit board 61′. However, both of the two driving means ineluctably increase the size of the LCD panel 610.